A current trend with mobile devices, and in particular mobile telephones and personal digital assistants (PDAs), is to provide them with multimodal interaction capabilities. Following this trend, it is anticipated by the inventors that some new devices will soon be provided with voice user interface capabilities. Such capabilities are expected to include text-to-speech (TTS) synthesis, which would allow a terminal to ‘speak’ text stored in a memory within itself or received over a communications channel and/or to play pre-recorded wave files, and automatic speech recognition (ASR), which would allow a terminal to understand instructions and information spoken by a user. However, such features would require considerable processing resources, and possibly also relatively large databases, which would present problems for developers of applications having voice user interface features.